The present invention relates to a touch panel disposed on the front of a display for use as a switch integrated therewith and a method of making such a touch panel.
FIG. 1A schematically represents, in perspective, the touch panel disclosed in Japanese Patent Application Publication Gazette No. 9-146707. In FIG. 1A a glass-glass touch panel is shown with its resistance film coated top and bottom glass substrates separately. A top glass substrate 11 is thinner than a bottom glass plate 12, and these substrates 11 and 12 are coated all over their opposing surface areas with transparent conductive films 13 and 14, respectively.
The transparent conductive films 13 and 14 serve as resistance films, which are formed by ITO or like films. Along opposite sides of the transparent conductive films 13 and 14 are formed electrodes 15, 16 and 17, 18, respectively.
In this example the electrodes 17 and 18 associated with the transparent conductive film 14 are disposed along its opposite sides in the X direction, whereas the electrodes 15 and 16 are disposed along the opposite sides of the transparent conductive film 13 in the Y direction. The electrodes 15 and 16 are extended in the X direction to form connecting pails 15a and 16a as shown.
On the glass substrate 12 there are formed lead-out patterns 21 and 22 extended from the electrodes 17 and 18 of die transparent conductive film 14, and their extended end portions arranged in a blank area at one side of the glass substrate 12 to form connecting terminals 21T and 22T. In order that the voltage to be applied across die electrodes 15 and 16 on the glass substrate 11 may be supplied from the connecting terminals on the glass substrate 12, or tat die voltage detected across the electrodes 15 and 16 on the glass substrate 11 may be taken out to die connecting terminals on die glass substrate 12, connecting portions 23a and 24a are formed on the glass substrate 12 in opposing relationship to connecting portions 15a and 16a provided at one end of the electrodes 15 and 16 on die glass substrate 11. Extended from the connecting portions 23a and 24a are lead-out patterns 23 and 24, whose extended ends are arranged as connecting terminals 23T and 24T side by side with the connecting terminals 21T and 22T.
The connecting terminals 23T and 24T of the lead-out patterns 23 and 24 are arranged together with the connecting terminals 21T and 22T along one side of the glass substrate 12; an FPC cable or the like (not shown) for circuit connection is connected to the portion where the connecting terminals are located. On the transparent conductive film 14 of the glass substrate 12 there are formed in proper alignment a number of dot spacers 25. According to the afore-mentioned Japanese patent application publication gazette, the glass substrates 11 and 12 are, for instance 0.2 mm and 1.1 mm thick, respectively, and have 130-by-133-mm outer dimensions. The dot spacers 25 are formed by screen printing photo-setting resin all over the transparent conductive film 14; for example, the dot spacers are 10 to 30 μm in diameter, 2 to 8 μm and spaced 2 to 8 mm apart. Pressed by a pointed stick from above, the glass substrate 11 is curved between adjacent dot spacers 25, bringing the transparent electrodes 13 and 14 into contact with each other. A similar touch panel structure is also disclosed in Japanese Patent Application Publication Gazette No. 10-133817.
The glass substrates 11 and 12 of such configurations as described above are integrated into a one-piece structure with their transparent conductive films 13 and 14 opposed, by joining the substrates 11 and 12 along their marginal edges through use of a sealer 26 containing a spacer material. The seal 26 is a mixer of a thermosetting resin, such as a resin of the epoxy series, and a spacer material. The sealer 26 is coated on the glass substrate 12 along its marginal edge as shown, and the glass substrate 11 is placed on and pressed onto the glass substrate 12, followed by firing the substrate assembly, thereby joining together the two glass substrate 11 and 12 with a required gap defined therebetween.
In this case, the connecting portions 15a and 16a of the electrodes 15 and 16 on the glass substrate 11 and the connecting portions 23a and 24a of the lead-out patterns 23 and 24 on the glass substrate 12 are held opposite vertically to the glass substrates 11 and 12, and connected to each other by conductive paste. In consequence, it is possible to supply voltage to the electrodes 15 and 15 on the glass substrate 11 from the connecting terminals 23T and 24T on the glass substrate 12 or take out to the connecting terminals 23T and 24T the voltages in the electrodes 15 and 16.
A notched portion 26a in the sealer 26 deposited on the glass substrate 12 along its marginal edge is used as a port for injecting air into the gap between the glass substrates 11 and 12 to swell the central portion of the glass substrate 11 and hence widen the gap centrally thereof after they are joined together. After the air injection, the notched portion 26a is sealed using resin.
The touch panel of the above configuration is adapted so that when depressed at an arbitrary point on the panel surface, the transparent conductive films 13 and 14 are pressed into contact with each other at that point By applying voltage across the transparent conductive film 14 and detecting its potential via the transparent conductive film 13, the X coordinate of the point of depression can be detected. Similarly, the Y-coordinate of that point can be detected by applying voltage across the transparent conductive film 13 and detecting its potential via die transparent conductive film 14. In this way, the X-Y coordinates at the point of depression can be detected.
In the touch panel of the above construction, for example, the connecting portion 16a formed on the glass substrate 11 and the connecting portion 24a on the glass substrate 12 are disposed at positions where they overlap each other in a direction vertical to the glass substrates 11 and 12 (that is, in the direction thickwise of the connecting portions 16a and 24a) as shown in FIG. 1B. The connecting portions 15a and 23a are also similarly formed. The conventional touch panel has such disadvantages as mentioned below.
That is, the electrodes 15 to 18 and the lead-out patterns 21 to 25 are formed by print-coating and firing conductive paste such as a silver paste of conductive particles (silver particles) having a particle size of around 6 μm. The electrodes 15 to 18 and the lead-out patterns 21 to 24 thus formed are approximately 10 μm thick.
On the other hand, the gap G defined by the glass substrates 11 and 12 therebetween is about 9 μm in the peripheral region of the panel; therefore, in the regions where the connecting portions 15a, 16a and 23a, 24a overlap, the gap becomes inevitably wider, distorting the thin glass substrate 11 and hence causing the Newton's rings and, at worst, breaking the glass substrate 11. Further, the nonuniformity in the gap width also causes variations in the pressure for actuating the touch panel.